The present invention generally relates to methods for electrically and mechanically connecting substrates. More particularly, it relates to a method for connecting and joining substrates employing a gallium intermetallic phase.
Substrates must be firmly connected to one another in various technical applications. For example, discrete semiconductor chips must thus be secured on carriers or heat sinks in chip mounting.
A further application arises in cubic integration. Substrates that contain integrated circuits, sensor structures or the like and that can be composed of different substrate materials and/or can be fabricated in different technologies are thereby ground thin to a few 10 .mu.m and are arranged as stacks. Contacts via which the circuit structures in the various substrates are connected to one another are formed in vertical direction. Such a component stack looks like a new semiconductor module when viewed from the outside. The neighboring substrates in the stack must be firmly connected to one another. Connections between contacts that meet one another from neighboring substrates must thereby also be formed.
European patent application EP 0 610 709 A has proposed that a refractory intermetallic phase be employed for connecting and through-contacting of substrates. This intermetallic phase is formed of a mixture of two metal constituents, the one thereof being liquid at the processing temperature and the other being solid and the solid constituent thereof dissolving in the liquid constituent, this leading to the hardening of the mixture. The mixture has completely solidified when the solidus curve in the phase diagram is upwardly transgressed. In German usage, such an intermetallic phase is referred to as amalgam insofar as the liquid constituent is composed of mercury. In the proposed method, however, the liquid constituent is not limited to mercury. In particular, it can be mercury, gallium or indium. The mixture is introduced into depressions that are respectively produced in neighboring substrates and that meet one another when the substrates are joined. The depressions are cast out with the liquid constituent. Excess material is removed by shaking or in an alternating electromagnetic field.